1. Field of the Invention
The invention relates to diagnostic and prognostic indicators and methods and reagents for their detection. The invention further relates to methods of monitoring the natural history of disease in a patient as well as methods for treating pathological conditions by vaccinating or administering antibodies specific for immunoglobulin cleavage sites to restore effector function of antibodies.
2. Description of the Related Art
In medicine, a biomarker is a biochemical substance that can be used to measure the progress of disease or the effects of treatment, that is, a diagnostic or prognostic indicator. One example is hemoglobin A1c which serves as a recent record of the excursion of blood glucose away from ideal levels as well as the duration of such excursions for glycemic control in diabetic patients.
Circulating immunoglobulins, and specifically those antibodies of the IgG class, are major serum proteins. It is well-known that human proteases are associated with inflammatory, proliferative, metastatic, and infectious diseases. Human proteases such as matrix metalloproteinases (MMPs) and neutrophil elastase cleave the IgGs heavy chain polypeptide at a residue unique to each protease as do bacterial proteases such as glutamyl endopeptidase (Staph. aureus) or immunoglobulin degrading enzyme of streptococcus (Strep. pyogenes). The cleavage sites in the heavy chain are clustered around the region termed the hinge domain, where the interchain disulfide linkage of the two heavy chains occurs. The region below the hinge constitutes the Fc region and comprises binding sites responsible for the effector functions of IgG. In the case of microorganisms, protease expression is a potential adjunctive virulence pathway allowing organisms to avoid opsonization (Rooijakkers et al. Microbes and Infection 7: 476-484, 2005) in so far as the proteolytic release of the Fc domain by cleavage below the hinge effectively neutralizes functions that would otherwise lead to the targeting and killing of that pathological cell. Thus, the elaboration of specific proteases may be representative of a myriad of diseases states including cancer, inflammation and infectious diseases.
That IgG degradation is enhanced in pathologic in vivo environments as evidenced by the presence of natural IgG autoantibodies that bind to the cleaved hinge domain (Knight et al., 1995; Nasu et al., 1980; Persselin and Stevens, 1985, Terness, et al. 1995 J Immunol. 154: 6446-6452). These autoantibodies also bind the Fab and F(ab′)2 fragments generated by several proteinases (including papain and pepsin), with particularly strong reactivity to the lower hinge domain remaining as C-terminal residues in F(ab′)2 molecules (Terness et al., 1995). The detection of the actual cleavage products have been reported (Fick et al., 1985; Goldberg and Whitehouse, 1970; Waller, 1974) but a robust assay which would allow these fragments to serve as biomarkers has not been developed possibly due to the low concentrations in serum resulting from rapid clearance of the various fragments or to technical problems in detecting the fragments amidst the large amount of intact immunoglobulin in blood and tissues. A specific antibody was prepared (Eckle, et al. 1988. Adv. Exp. Med. Biol. 240: 531-534) for detection of human neutrophil elastase cleaved Fc domain detected Fc at a median concentration of 0.62 ug/ml directly in synovial fluid of rheumatoid arthritis patients but not in synovial fluid from patients with other types of joint disease.
Therefore, the ability to assess the type and amount of IgG cleavage product(s) in the bodily fluids or blood of subjects could be used as a biomarker of specific disease activity. Specific reagents and methods for such determinations would provide useful tools for diagnostic and prognostic medical assays. Further, the ability to correct loss of IgG functions in vivo due to cleavage and the ability to compensate the process of IgG cleavage in the body of subjects suffering from protease specific disease activity has not been heretofore envisioned as a therapeutic strategy.